Efficient and Low-Carbon Synthesis of Colorless Transparent Polyimides

Abstract

The widespread use of polyimide varnish in semiconductors, packaging, and flexible displays has created increasing demand for efficient and environmentally friendly preparation. Compared to polyamic acid varnish, polyimide varnish offers enhanced stability and significantly improved process control, as it eliminates the need for chemical reactions during subsequent production steps. However, traditional polyimide varnish synthesis involves the preparation of polyamic acid followed by chemical imidization, a complex and time-consuming process that includes precipitation, washing, and dissolution. This method is not only costly but also poses environmental and safety risks. In this study, we propose a high-temperature one-step process to prepare a colorless polyimide varnish using the environmentally friendly solvent 3-methoxy-N,N-dimethylpropanamide (MDMPA), and benzoic acid as a catalyst. The process requires only 4 h to obtain high molecular weight polyimide varnish without aftertreatment. The varnish can be easily converted into a transparent film through low-temperature drying. Additionally, by introducing a small amount of 3,5-diaminobenzoic acid (DABA) for copolymerization, polyimide synthesis can be successfully achieved without external catalysts. The resulting polyimide exhibits a higher imidization degree and significantly improved peel strength between the polyimide and copper foil. This one-step process not only maintains the superior properties of colorless transparent polyimides (CPI) but also reduces reliance on toxic solvents, enhances production efficiency, and provides an environmentally sustainable solution for the large-scale production of high-performance polyimides.